There is an engine known from Japanese Patent Application Laid-open No. 3-64658, in which an upper space in a subsidiary tank for temporarily storing fuel to be supplied to a fuel injection valve is connected to a portion near a throttle valve through an air vent pipe.
In the known engine, there is a possibility that the vapor of fuel discharged from the subsidiary tank through the air vent pipe into an intake system may be liquefied within a throttle body, when the engine is stopped.